1. Field of the Invention
This invention relates to a data carrier printed by intaglio printing, to the production thereof and to a printing plate suitable therefor and the method for producing said plate.
2. Description of Related Art
Security documents and documents of value, for example bank notes, shares, bonds, certificates, vouchers and the like, which must meet high standards with respect to forgery-proofness, are frequently printed by intaglio printing. This printing process provides a characteristic printed image that is easily recognizable to laymen and cannot be imitated with other common printing processes.
In intaglio printing, surfaces are usually rendered by a line screen, the line distance and width determining the color tone or gray value of the surface. Printed lines are usually a few tenths of a millimeter wide and separated by unprinted areas. During the printing operation, only the depressions formed in the printing plate surface by means of etching or engraving carry ink, while the actual printing plate surface is ink-free. This is obtained by wiping the printing plate surface free of excess ink after inking with a wiping cylinder or doctor blade.
During the actual printing operation the data carrier to be printed is pressed against the printing plate with high pressure by a pressure cylinder with an elastic surface. The at least partly compressible data carrier, usually made of paper, is thereby pressed into the ink-filled depressions of the printing plate and thus comes in contact with the ink. When the data carrier is detached from the printing plate, the latter pulls the ink out of the depressions. A printed image produced in this way has spaced-apart printed lines or areas that are covered with an ink layer of varying thickness in accordance with the depth of the printing plate engraving.
The high bearing pressure additionally causes the substrate material to undergo an embossing that is also noticeable on the back of the data carrier. If the engravings in the printing plate are deep enough, a data carrier printed by intaglio printing acquires through embossing and inking a printed image that forms a relief perceptible with the sense of touch. In the unprinted surface areas of the data carrier not carrying ink, the high pressures during the printing operation act like a calendering, which leads to compression and smoothing of the data carrier surface. These features make prints produced by intaglio printing distinguishable anytime from prints produced by other techniques.